1. Field of the Invention
The present invention generally relates to telecommunications and, more particularly, to an apparatus and method for combining POTS and DSL apparatus and function into one device. The combination uses a single highspeed CODEC which samples both the POTS signal and the DSL signal.
2. Description of the Invention
As known in the art, high-speed modems are able to transfer data at high rates over a local loop. In order to accomplish these high data rates, the high-speed digital modems use frequencies which are significantly higher than the voice band frequencies used in the plain old telephone system (xe2x80x9cPOTSxe2x80x9d).
However, such modems require that the central office wire center utilize a POTS splitter device to separate the POTS voice band frequencies, occurring in the frequency spectrum between about 0 Hz and about 4 kHz, from the highspeed digital modem data using the frequency spectrum of between about 20 kHz and about 1 MHz. This setup also requires that there be duplicative hardware to process the POTS voice and digital modem frequencies. The hardware converts the voice data into digital data for transmission over a voice time division multiplexing (TDM) bus, and the digital signal that is processed by analog front end and coder/decoder (CODEC) devices converts the highspeed modem data from the analog frequencies back to digital data. Unfortunately, the manufacture and installation of POTS filters and duplicative coder/decoder and analog front end logic are expensive and their use sometimes requires the rewiring of the central office wire center.
Consequently, it would be desirable to avoid the use of the POTS splitter and duplicative analog front-end and coder/decoder logic, which saves space due to the reduced circuitry and avoids the expense the extra circuitry imposes.
Certain objects, advantages and novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the advantages and novel features, the present invention is generally directed to a central office data communications apparatus and method, that allows a combined voice POTS and high speed modem processing functions into one device at the central office. The combination of the signals allows for a single high-speed CODEC which samples both a POTS signal and the high-speed modem signals to be utilized. This eliminates the need for external POTS splitters and costly duplicative circuitry.
One embodiment of the modem apparatus and method for a combined digital subscriber line (DSL) and voice system includes apparatus for processing the voice POTS signals and the speed modem signals through a common analog front end high-speed coder/decoder (CODEC) circuitry. The digital signals from the high-speed CODEC are provided to a DSP logic which provides for support of multiple voice lines. Once connected, voice POTS frequencies are not bursty, and therefore, need to be serviced on an eight kHz sample rate in both directions. The digital signal processor (DSP) provides this processing by filtering between voice and high speed modem data in the DSP itself.
The preferred embodiment includes a sample rate of 192 kHz. However, any sample rate is possible as long as it is a multiple of the eight kHz, because the voice POTS signal is always sampled at an eight kHz rate in order to interface to the public switched telephone network (PSTN) network. Since the conversion and filtering between voice and high speed modem data is not run time extensive, the DSP can service multiple subscriber lines simultaneously without saturation.
The invention can also be viewed as providing a method for allowing combined voice POTS and high speed modem processing functions in one device. In this regard, the method can be broadly summarized by the following steps:
interfacing to a local loop capable of simultaneously carrying both a POTS signal and high speed modem signals;
sampling both said POTS and said high speed modem signals with a single codec; and
processing both said sampled POTS and said sampled modem signals.